The present invention relates to a waterstop sealing material comprising a foamed structure having closed cells or both closed cells and open cells.
A rubber foamed product has excellent cushioning properties and thus can be used as a cushioning material, padding material or the like. The comparison of closed cells and open cells in a foamed structure shows that the former is a structure having cells defined by a steric lattice as a partition and the latter is a structure having cells free of partition. The latter structure can be easily deformed dynamically. However, the open cell type foamed structure cannot be expected to have waterstop action while the closed cell type foamed structure can be expected to have waterstop action because of repulsive power developed by the partition between cells.
A foamed structure having both closed cells and open cells (hereinafter occasionally referred to as xe2x80x9csemi-closed and semi-open foamed structurexe2x80x9d) can be expected to have both ease in filling complex voids developed by the high deformability based on open cells and good waterstop properties based on closed cells. Thus, such a foamed structure can be used as a waterstop sealing material having complex voids which are filled before use.
However, the foregoing closed foamed structures or semi-closed and semi-open foamed structures are disadvantageous in that when used as waterstop sealing material, they are liable to show a relaxed repulsive power as foamed structure with time, lowering the contact pressure between the surface of the foamed structure and the surface of the adherend and hence causing water leakage along the interface. Thus, these foamed structures occasionally cannot act to stop water. In order to solve these problems, an approach has been proposed involving the provision of a pressure-sensitive adhesive layer on both sides of the foamed structure allowing sealing of the interface of the adherend. However, when a general acrylic or rubber pressure-sensitive adhesive is used as a pressure-sensitive adhesive layer, it exhibits adhesion at the same time with mounting, making it difficult for the waterstop sealing material to be repositioned and hence causing troubles in sealing operation.
JP-A-10-77463 (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) discloses that when a pressure-sensitive adhesive layer mainly composed of a polymer having a polycarbonate structure is used as a pressure-sensitive adhesive layer to be provided on the closed foamed structure or semi-closed or semi-open foamed structure, the resulting waterstop sealing material is not immediately bonded to the adherend because the pressure-sensitive adhesive layer is tack-free, can be easily repositioned and mounted without any trouble and then can be gradually bonded to the adherend by the repulsive power of the foamed structure to give drastically enhanced sealing properties between the surface of the foamed structure and the interface of the position to be processed.
However, even the foregoing waterstop sealing material causes deterioration in sealing properties during use under severe conditions, i.e., high temperature over an extended period of time.
It is therefore an object of the present invention to further improve the foregoing proposed waterstop sealing material and hence provide a shaped waterstop sealing material (namely, a solid and non-flowable sealing material unlike a caulking compound) having further improvements in sealing properties.
The inventors made extensive studies of the foregoing object. As a result, it was found that when used under severe conditions, i.e., high temperature over an extended period of time, waterstop sealing materials are liable to the migration of certain components in some foamed structures to the pressure-sensitive adhesive layer mainly composed of a polymer having a polycarbonate stricture, thereby causing the deterioration of the foregoing pressure-sensitive adhesive layer and lowering of the adhesion and resulting in the deterioration of the sealing properties of the waterstop sealing materials.
Furthermore, it was found that when the specific pressure-sensitive adhesive layer mainly composed of a polymer having a polycarbonate structure is provided on the foamed structure through another pressure-sensitive adhesive layer made of rubber or acrylic pressure-sensitive adhesive or a base material interposed between the specific pressure-sensitive adhesive layer and the foamed structure as a subbing layer, the tack-freeness of the upper pressure-sensitive adhesive layer makes it possible to improve the sealing operation such as mounting. Further, the subbing pressure-sensitive adhesive layer or base material prevents the migration of components from the foamed structure, making it possible to avoid the deterioration of the upper pressure-sensitive adhesive layer. Even when the foregoing components migrate to the subbing pressure-sensitive adhesive layer, there arises little or no disadvantages such as deterioration. Eventually, this arrangement exhibits further enhancement of sealing properties as compared with those comprising an upper pressure-sensitive adhesive layer alone. In particular, this arrangement provides excellent sealing properties under severe conditions, i.e., high temperature over an extended period of time.
The present invention provides a waterstop sealing material comprising a foamed structure having closed cells or both closed cells and open cells, the foamed structure having a multi-layer pressure-sensitive adhesive layer provided on at least one side thereof, the multi-layer pressure-sensitive adhesive layer comprising as an outermost layer a layer made of a pressure-sensitive adhesive composition containing a polymer having a polycarbonate structure having a repeating unit represented by the following general formula: 
wherein R represents a C2-20 straight-chain or branched hydrocarbon group and n represents a positive integer. The present invention further concerns a waterstop sealing material having the foregoing structure, wherein the foamed structure has a multi-layer pressure-sensitive adhesive layer provided on at least one side thereof, the multi-layer pressure-sensitive adhesive layer comprising as an outermost layer a layer made of a pressure-sensitive adhesive composition containing a polymer having a polycarbonate structure, and a pressure-sensitive adhesive layer made of a pressure-sensitive adhesive composition different from the pressure-sensitive adhesive composition provided on the other side thereof.
The present invention further provides a waterstop sealing material comprising a foamed structure having closed cells or both closed cells and open cells, the foamed structure having a layer made of a pressure-sensitive adhesive composition containing a polymer having a polycarbonate structure having a repeating unit represented by the following general formula provided on at least one side thereof with a base material interposed therebetween: 
wherein R represents a C2-20 straight-chain or branched hydrocarbon group and n represents a positive integer. The present invention further concerns a waterstop sealing material having the foregoing structure, wherein the foamed structure has a layer made of a pressure-sensitive adhesive composition containing a polymer having a polycarbonate structure provided on one side thereof with a base material interposed therebetween and a pressure-sensitive adhesive layer made of a pressure-sensitive adhesive composition different from the pressure-sensitive adhesive composition provided on the other side thereof.